Q. Explain working of Shaded-pole motors?

Shaded-pole motors: The least expensive of the fractional-horsepower motors, generally rated up to 1 / 20 hp, they have salient stator poles, with one-coil-per-pole main windings. The auxiliary winding consists of one (or rarely two) short-circuited copper straps wound on a portion of the pole and displaced from the center of each pole, as shown in Figure (a). The shaded-pole motor got its name from these shading bands. Induced currents in the shading coil cause the flux in the shaded portion of the pole to lag the flux in the other portion in time. The result is then like a rotating field moving in the direction from the unshaded to the shaded portion of the pole. A low starting torque is produced. A typical torque-speed characteristic is shown in Figure (b). Shaded-pole motors have a rather low efficiency.